The invention relates to turbine assembly components, such as an airfoil. More particularly, the invention relates to a turbine assembly having a hybrid structure. Even more particularly, the invention relates to articles, such as airfoils, having an oxidation resistant hybrid structure for a turbine assembly.
Turbine assemblies, such as aeronautical turbines, land-based turbines, marine-based turbines, and the like, typically include components formed from a class of materials known as superalloys. Superalloys exhibit desirable chemical and physical properties under the high temperature, high stress, and high-pressure conditions generally encountered during turbine operation. Nickel (Ni), iron (Fe), and cobalt (Co)-base superalloys are of particular interest in such applications. For example, turbine components, such as an airfoil, in modern jet engines can reach temperatures as high as about 1,150xc2x0 C., which is about 85% of the melting temperatures of most Ni-based superalloys.
At high service temperatures, the superalloys that are used to form the turbine components are highly susceptible to damage from such mechanisms as creep, oxidation, and melting. The application of thermal barrier coatings, typically formed from a refractory material, to the component surface enhances the performance of superalloys at high temperature by reducing the temperature at the metal surface. Although such coatings offer a measure of protection, they are subject to chipping, cracking, and spalling.
The problems associated with material melting points and oxidation resistance are exacerbated by state-of-the-art turbine designs, which call for higher operating temperatures in order to boost turbine efficiency. In advanced design concepts, the surface temperatures of components are expected to exceed the melting points of state-of-the-art superalloys. Therefore, what is needed is a turbine component, such as an airfoil, having improved high-temperature capabilities relating to such parameters as, for example, melting point and oxidation resistance. Due to the often high costs associated with materials exhibiting sufficient high-temperature capabilities, an additional need is for the component to be cost effective.
The present invention provides embodiments that address these needs. A first embodiment is an article for use in a hot gas path of a gas turbine assembly. The article comprises: a spar, the spar providing mechanical support for the article and comprising a cooling fluid delivery system, a top end, and a bottom end; a standoff structure attached to the spar, the standoff structure comprising a plurality of spacing elements in a spaced-apart relation to each other, the spacing elements having first ends adjacent to the spar and second ends opposite to the first ends; a skin conformally surrounding the spar and the standoff structure, the skin comprising a top end and a bottom end, wherein the standoff structure separates the spar and the skin, wherein the plurality of spacing elements is disposed with an inner surface of the skin adjacent to the second ends of the spacing elements to form a plurality of plena between the spar and the skin, the plena in fluid communication with the cooling fluid delivery system, the skin comprising at least one metal selected from the group consisting of Rh, Pd, and Pt; and a base connecting the bottom end of the spar and the bottom end of the skin.
A second embodiment is a metallic skin for an article located in the hot gas path of a gas turbine assembly. The skin comprises a free-standing sheet comprising at least one metal selected from the group consisting of Rh, Pd, and Pt; wherein the sheet has a shape adapted to conformally surround a support structure of the article.
A third embodiment is a method for making an article for use in a hot gas path of a gas turbine assembly. The method comprises: providing a spar, the spar providing mechanical support for the article and comprising a cooling fluid delivery system, a top end, and a bottom end; attaching a standoff structure to the spar, the standoff structure comprising a plurality of spacing elements in a spaced-apart relation to each other, the spacing elements having first ends adjacent to the spar and second ends opposite to the first ends; providing a skin conformally surrounding the spar and the standoff structure, the skin comprising a top end and a bottom end, wherein the standoff structure separates the spar and the skin, wherein the plurality of spacing elements is disposed with an inner surface of the skin adjacent to the second ends of the spacing elements to form a plurality of plena between the spar and the skin, the plena in fluid communication with the cooling fluid delivery system, the skin comprising at least one metal selected from the group consisting of Rh, Pd, and Pt; providing a base for the article; and joining the bottom end of the spar and the bottom end of the skin to the base.